In recent years, interest in energy conservation measures increases and development of a near-infrared light reflective film for blocking the transmission of heat rays in the sunlight from window glass of buildings and vehicles has been actively performed, because it can reduce the load on cooling installation and is effective as an energy conservation measure.
Conventionally, it has been proposed to manufacture, as a near-infrared light reflective films, a laminated film obtained by alternately laminating a high refractive index layer and a low refractive index layer, in a dry film formation method such as vapor deposition and sputtering. Further, it has been known that by adjusting the optical film thickness of the laminated film obtained by alternately laminating layers, the film can be designed to reflect visible light instead of the near-infrared light.
However, a dry film formation method has problems such as a high manufacturing cost, difficulty in area enlargement, and limitation in a heat-resistant material.
Therefore, as a manufacturing method by a coating method, a method of using a thermosetting resin (Patent Literature 1) and a method of using a UV curable resin (Patent Literature 2) are disclosed. These methods are advantageous in terms of a manufacturing cost and area enlargement, but the both methods use a large amount of an organic solvent and are not preferable in terms of environmental conservation.
In the production of near-infrared light reflecting films, there is little known example of using an aqueous coating solution using a water-soluble polymer. As it were, there is a description of spin-coating with an aqueous solution in formation of a low refractive index layer in examples of Patent Literature 3. However, the solution is not a solution to which inorganic oxide particles are added, and a high refractive index layer is formed by spin coating an organic solvent (PGMEA; Propylene Glycol Monomethyl Ether Acetate) solution containing TiO2+dispersing agent+UV curable resin, which is not water-based coating. There is also a description that a high refractive index layer is formed by spin coating a water-ethanol (20:80) mixed solvent containing ZnO2+polyvinyl pyrrolidone in examples of Patent Literature 4.
Meanwhile, a method of manufacturing a laminated film of two or more layers on a substrate by coating generally includes sequential coating of laminating layers one by one by coating and drying and simultaneous multilayer coating of coating plural layers simultaneously. The sequential coating includes a spin coating method, a bar coating method, blade coating, and gravure coating and has low productivity because the number of coating and drying increases in the case of creating a multilayered film such as an optical reflective film. On the other hand, the simultaneous multilayer coating includes a method using curtain coating and slide bead coating and has high productivity because plural layers can be formed simultaneously.